The present invention relates to a process for directly reducing iron ore in a rotary kiln using a solid, carbonaceous material, such as coal, as both fuel and reductant and, more particularly, to a method and means for maintaining a temperature profile within the kiln bed for eliminating sintering of the charge.
Many different methods have been suggested and used for carrying out the direct reduction of ores containing iron oxide using carbonaceous materials, particularly coal, as both the heating agent and reductant in a rotary kiln. For example, in some of these processes the coal is fed into the kiln through the discharge end by mechanical or pneumatic means, such as respectively disclosed in U.S. Pat. No. 3,113,859 to Moklebust and U.S. Pat. No. 3,505,060 to Heitmann, and in some it is fed at the center of or along the kiln, such as disclosed in U.S. Pat. No. 3,206,299 to Senior et al. However, considerable problems have been encountered with these various approaches, many of which problems have been overcome by the process disclosed in U.S. Pat. No. 3,890,138 to Hockin. In this latter process a portion of the coal is injected or blown from the discharge end of the kiln, and the remaining portion of the coal is fed with the ore at the charge feed end. The kiln is generally divided into a reducing zone toward the discharge end and a preheat zone toward the feed end, and the coal is distributed in the kiln in such a manner that the amount of coal injected from the discharge end is sufficient to aid in controlling the temperature profile throughout both zones of the kiln.
Although the process of Hockin was developed particularly for use in reducing ilmenite, it has been found that the dual end coal feeding technique improves upon the other coal feeding methods used in reducing iron ore to sponge iron in rotary kilns with the direct reduction process. The present invention relates to improvements in this latter process when dual end coal feeding is used but is readily applicable for use in kilns with other reductant feeding techniques as well.